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<html>
  <head>
    <meta charset="UTF-8">
    <title>Document</title>
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  <body>
    <script>
      console.log(1);
      setTimeout(function () {
        console.log(3);
      }, 0);
      for (var i = 0, str = ''; i < 900000; i++) {
        str += i;		// 利用字符串拼接运算拖慢执行时间
      }
      console.log(2);
    </script>
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